When Joe Darby saw the horrific photos of abuse at Abu Ghraib prison he was stunned.

So stunned that he walked out into the hot Baghdad night and smoked half a dozen cigarettes and agonised over what he should do.

Joe Darby was a reserve soldier with US forces at Abu Ghraib prison when he stumbled across those images which would eventually shock the world in 2004.

They were photographs of his colleagues, some of them men and women he had known since high school - torturing and abusing Iraqi prisoners.

His decision to hand them over rather than keep quiet changed his life forever.

The military policeman has only been allowed to talk about that struggle very recently, and in his first UK interview, for BBC Radio 4's The Choice, he told Michael Buerk how he made that decision and how he fears for the safety of his family.

Photos of abuse

He had been in Iraq for seven months when he was first handed the photographs on a CD. It was lent to him by a colleague, Charles Graner.

I knew that some people wouldn't agree with what I did... They view it as - I put American soldiers in prison over Iraqis

Joe Darby

Most of the disc contained general shots around Hilla and Baghdad, but also those infamous photos of abuse.

At first he did not quite believe what he was looking at.

"The first picture I saw, I laughed - because one, it's just a pyramid of naked people - I didn't know it was Iraqi prisoners," he says.

"Because I have seen soldiers do some really stupid things. As I got into the photos more I realised what they were.

"There were photos of Graner beating three prisoners in a group. There was a picture of a naked male Iraqi standing with a bag over his head, holding the head, the sandbagged head of a male Iraqi kneeling between his legs.

"The most pronounced woman in the photographs was Lynndie England, and she was leading prisoners around on a leash. She was giving a thumbs-up and standing behind the pyramid, you know with the thumbs-up, standing next to Graner. Posing with one of the Iraqi prisoners who had died."

Promised anonymity

Joe Darby knew what he saw was wrong, but it took him three weeks to decide to hand those photographs in. When he finally did, he was promised anonymity and hoped he would hear no more about it.

Mr Darby feared repercussions from the soldiers in the photos

But he was scared of the repercussions from the accused soldiers in the photos.

"I was afraid for retribution not only from them, but from other soldiers," he says.

"At night when I would sleep, they were less than 100 yards from me, and I didn't even have a door on the room I slept in.

"I had a raincoat hanging up for a door. Like I said to my room mate, they could reach their hand in the door - because I slept right by the door - and cut my throat without making a noise, or anybody knowing what was going on, and I was scared of that."

When the accused soldiers were finally removed from the base, he thought his troubles were over.

And then he was sitting in a crowded Iraqi canteen with hundreds of soldiers and Donald Rumsfeld came on the television to thank Joe Darby by name for handing in the photographs.

"I don't think it was an accident because those things are pretty much scripted," Mr Darby says.

"But I did receive a letter from him which said he had no malicious intent, he was only doing it to praise me and he had no idea about my anonymity.

"I really find it hard to believe that the secretary of defence of the United States has no idea about the star witness for a criminal case being anonymous."

Rather than turn on him for betraying colleagues, most of the soldiers in his unit shook his hand. It was at home where the real trouble started.

Labelled a traitor

His wife had no idea that Mr Darby had handed in those photos, but when he was named, she had to flee to her sister's house which was then vandalised with graffiti. Many in his home town called him a traitor.

"I knew that some people wouldn't agree with what I did," he says.

"You have some people who don't view it as right and wrong. They view it as: I put American soldiers in prison over Iraqis."

That animosity in his home town has meant that he still cannot return there.

After Donald Rumsfeld blew his cover, he was bundled out of Iraq very quickly and lived under armed protection for the first six months.

He has since left the army but did testify at the trials of some of those accused of abuse and torture. It is Charles Graner he is most afraid of.

"Seeing Graner across the courtroom was the only one that was difficult during the trial," he says.

"He had a stone-cold stare of hatred the entire time - he wouldn't take his eyes off me the whole time he sat there. I think this is a grudge he will hold till the day he gets out of prison."

Mr Darby and his family have moved to a new town. They have new jobs. They have done everything but change their identities.

But he does not see himself as a hero, or a traitor. Just "a soldier who did his job - no more, no less".

"I've never regretted for one second what I did when I was in Iraq, to turn those pictures in," he says.

You can hear Joe Darby being interviewed by Michael Buerk on BBC Radio 4's The Choice on 7 August at 0900 BST.